The present invention relates to apparatus for utilization in presses for shaping and curing tires. More particularly, the present invention relates to apparatus for positioning an uncured tire relative to a press for shaping and curing tires wherein the uncured tire is positioned and manipulated by a unique bag control or center mechanism configuration. More specifically, the invention relates to apparatus for processing an uncured tire in a tire shaping and curing press in which a unique form of diaphragm type center mechanism is employed in a manner which may be particularly advantageous in conjunction with the processing of radial tires.
Although numerous types of presses for shaping and curing tires have been developed over the years, the most universally acceptable have employed center mechanisms which utilize a flexible, generally cylindrical bladder or diaphragm member which is secured to the press and is capable of being radially distended within an uncured tire band in order to apply shaping pressure and curing pressure and heat to the interior surface of the tire band. The inventor's assignee has pioneered in the development of numerous forms of such tire shaping and curing presses and manufactures the wellknown and highly regarded press sold under the trademark "Bag-O-Matic".
Radial tires have met with substantial success abroad for many years and have been gaining increased acceptance domestically over the past few years. Radial ply tires as well as belted/bias ply tires both incorporate an annular, inextensible breaker ply or belt that extends circumferentially of the carcass beneath the tread ply. Tires of such configuration normally are not built in the cylindrical form of a conventional bias ply tire, which was the industry standard for many years, because of the inextensible nature of the breaker ply employed in such tires. Rather, the carcass must be at least partially pre-shaped before the breaker ply is positioned and affixed. In such pre-shaped uncured tire bands the bead forming portions are therefore necessarily in closer axial proximity to each other in that the pre-shaped tire band approximates to some extent the configuration of a cured tire as contrasted with the substantially cylindrical configuration of conventional bias ply tires. Therefore, the bead to bead dimension interiorly of such a preformed tire substantially exceeds the axial distance between the beads. Accordingly, a bladder or diaphragm member which has an axial extent that approximates the bead to bead dimension interiorly of a tire will when axially extended to receive the tire thereover project a substantial distance above the upper bead of the tire.
In early industry experience with the insertion of a bladder in such a pre-shaped tire band substantial difficulty was encountered in that either the bladder or the upper bead of the tire or both were critically damaged. This problem was solved in a manner and employing apparatus which has become substantially in industry standard as disclosed in U.S. Pat. No. 2,997,738.
Recently, the industry has evidenced an interest in increasing pressure and temperature characteristics of the curing medium inserted in the bladder due to considerations of construction and constitution of pre-shaped uncured tire bands and for purposes of reducing the cure time, thereby increasing press productivity.
The manipulation of the bladder and related center mechanism components in most prior art presses has been accomplished hydraulically, i.e., by one or more hydraulic cylinders positioned within the press proximate the center mechanism components. Inasmuch as water is chemically neutral to the exposed components of a tire as well as the elastomer, normally rubber, from which the bladder is made it is most commonly employed as the hydraulic fluid. The use of water as the hydraulic fluid is advantageous with respect to many operational considerations of a cylinder and is otherwise most satisfactory so long as the seal between the cylinder and the interior of the bladder effectively precludes any leakage. However, if the water or other hydraulic fluid from the cylinder does penetrate into the bladder, as, for example, when the bladder is extended to effect removal of a cured tire, the residual heat of the center mechanism components from the previous curing cycle is sufficient to cause the water to flash into steam which tends to inflate or radially puff out the bladder. Such radial expansion may be sufficient to impede removal of a cured tire or the positioning of an uncured tire band such as to cause damage to either the tire or press components. Another critical time is during the shaping of the uncured tire band when a relatively low pressure fluid, normally steam, is inserted in the diaphragm and radial puffing or pressure fluctuation may cause improper seating of the bladder in the uncured tire band.
Another problem may be encountered during the final cure of the tire under the above-mentioned increased pressure and temperature conditions wherein high pressure water is employed as the curing medium. The penetration of the curing medium through the seals into the operating cylinder can result in contamination of the hydraulic fluid in a cylinder which eventually produces operational difficulties.
Although mechanical arrangements have been proposed to eliminate the use of a cylinder in proximity with the bladder, such devices tend to substantially increase the complexity of the center mechanism configuration, require additional space, reduce the operating flexibility with respect to other features which may be provided and have otherwise proved to be unacceptable.